My trailer only came with one battery cave, at some point my grand father had an identical one added to the other side. Since taking ownership I have thought about adding a third and fourth battery at an angle off the first box.

I also am comtemplating additional battery capacity. I currently have the single battery compartment. Rather than add a second, and a third and a fourth, my thinking is to have a single 8D Lifeline AGM right in the middle. Venting (tho not needed) will be easy. I will have to relocate the crappy univolt which I am replacing anyways. In my 78 Tradewind there seems to be just enough (and I mean just enough) room for this.

Tongue weight will go up in the range of 60 pounds since I remove a battery and the old vacuum hydraulic brake actuator.

I currently have a Lifeline 8D in my 67 safari, it has worked out great.

Due to the problems posed by mixing AGM and flooded types it would be necessary for me to replace the two existing batteries with AGMs if I plan to continue using them.

Bottom line the AGM batteries cost $2.50 an amp hour while flooded batteries cost $1.50 an amp hour. This is a recurring cost. For a 500 AH battery string this is a $500 cost difference every five years. It is for this reason that I am exploring the possibility of adding compartments, or, to ck's point, expanding the existing ones.